Microfabrication using patterned topography and self-assembled monolayers

ABSTRACT

A method of selectively and electrolessly depositing a metal onto a substrate having a metallic microstructured surface is disclosed. The method includes forming a self-assembled monolayer on the metallic microstructured surface, exposing the self-assembled monolayer to an electroless plating solution including a soluble form of a deposit metal, and depositing electrolessly the deposit metal selectively on the metallic microstructured surface. Article formed from this method are also disclosed.

This application is a divisional of U.S. Ser. No. 11/003,233, filed Dec.3, 2004, now U.S. Pat. No. 7,160,583 now allowed, the disclosure ofwhich is incorporated by reference in its entirety herein.

BACKGROUND

The present disclosure relates to a method of fabricating patternedmetallic deposits on substrates and the articles so fabricated.

Polymeric films with patterns of metallic material have a wide varietyof commercial applications. In some instances, it is desired that aconductive grid be sufficiently fine to be invisible to the unaided eyeand supported on a transparent polymeric substrate. Transparentconductive sheets have a variety of uses including, for example,resistively heated windows, electromagnetic interference (EMI) shieldinglayers, static dissipating components, antennas, touch screens forcomputer displays, and surface electrodes for electrochromic windows,photovoltaic devices, electroluminescent devices, and liquid crystaldisplays.

The use of essentially transparent electrically conductive grids forsuch applications as EMI shielding is known. The grid can be formed froma network or screen of metal wires that are sandwiched or laminatedbetween transparent sheets or embedded in substrates (U.S. Pat. Nos.3,952,152; 4,179,797; 4,321,296; 4,381,421; 4,412,255). One disadvantageof using wire screens is the difficulty in handling very fine wires orin making and handling very fine wire screens. For example, a 20 microndiameter copper wire has a tensile strength of only 1 ounce (28 gramsforce) and is therefore easily damaged. Wire screens fabricated withwires of 20 micron diameter are available but are very expensive due tothe difficulty in handling very fine wire.

Rather than embed a preexisting wire screen into a substrate, aconductive pattern can be fabricated in-situ by first forming a patternof grooves or channels in a substrate and then filling the grooves orchannels with a conductive material. This method has been used formaking conductive circuit lines and patterns by a variety of means,although usually for lines and patterns on a relatively coarse scale.The grooves can be formed in the substrate by molding, embossing, or bylithographic techniques. The grooves can then be filled with conductiveinks or epoxies (U.S. Pat. No. 5,462,624), with evaporated, sputtered,or plated metal (U.S. Pat. Nos. 3,891,514; 4,510,347; and 5,595,943),with molten metal (U.S. Pat. No. 4,748,130), or with metal powder (U.S.Pat. Nos. 2,963,748; 3,075,280; 3,800,020; 4,614,837; 5,061,438; and5,094,811). Conductive grids on polymer films have been made by printingconductive pastes (U.S. Pat. No. 5,399,79) or by photolightography andetching (U.S. Pat. No. 6,433,481). These prior art methods havelimitations. For example, one problem with conductive inks or epoxies isthat the electrical conductivity is dependent on the formation ofcontacts between adjacent conductive particles, and the overallconductivity is usually much less than that of solid metal. Vapordeposition of metal or electroplating is generally slow and oftenrequires a subsequent step to remove excess metal that is depositedbetween the grooves. Molten metal can be placed in the grooves butusually requires the deposition of some material in the grooves that themetal will wet. Otherwise the molten metal will not penetrate nor stayin the grooves due to surface tension of the molten metal.

Circuits have been made by placing metal powder into grooves followed bycompacting the powder to enhance electrical contact between theparticles. Lillie et al. (U.S. Pat. No. 5,061,438) and Kane et al. (U.S.Pat. No. 5,094,811) have used this method to form printed circuitboards. However, these methods are not practical for making finecircuits and fine metal patterns. One a fine scale, replacing orre-registering the tool over the embossed pattern to perform the metalcompaction can be difficult. For example, a sheet with a pattern of 20micron wide channels would require that the tool be placed over thepattern to an accuracy of roughly 3 microns from one side of the sheetto the other. For many applications, the sheet may be on the order of 30cm by 30 cm. Dimensional changes due to thermal contraction of athermoplastic sheet are typically about 1 percent or more during coolingfrom the forming temperature to room temperature. Thus, for a 30 cm by30 cm sheet, a contraction of 1 percent would result in an overallshrinkage of 0.3 cm. This value is 1000 times larger than the 3 micronplacement accuracy needed, making accurate repositioning of the tooldifficult.

SUMMARY

The present disclosure relates to articles that include a substrate witha patterned metallic deposit. More specifically, the articles areprepared by selectively and electrolessly depositing a metal onto asubstrate having a metallic microstructured surface.

A first aspect relates to a method that includes providing a substratethat has a metallic microstructured surface, forming a self-assembledmonolayer on the metallic microstructured surface, exposing theself-assembled monolayer to an electroless plating solution thatcontains a soluble form of a deposit metal, and depositing electrolesslythe deposit metal selectively on the metallic microstructured surface.

Various methods can be used to form the substrate with a metallicmicrostructured surface. In one embodiment, the microstructure can beformed on a metallic surface with a mechanical tool. The mechanical toolcan emboss, scribe, or mold the microstructure onto the metallicsurface. In a further embodiment, the microstructure can be formed in asubstrate surface with a mechanical tool and then a metal layer can bedisposed on the microstructured surface to form a metallicmicrostructured surface. The mechanical tool can emboss, scribe or moldthe microstructure onto the substrate surface. In yet a furtherembodiment, the microstructure can be formed in a substrate surface bydepositing a metal onto the substrate surface or by removing metal froma metallic substrate surface.

In another aspect, an article is provided. In one embodiment, thearticle includes a substrate having a substrate surface and atopographical feature disposed on the substrate surface. A continuoushomogenous metal layer is disposed on the substrate surface adjacent thetopographical feature and on the topographical feature. A self-assembledmonolayer is disposed on the continuous homogenous metal layer, and adeposit metal is disposed on the continuous homogenous metal layer onthe topographical feature, and is not disposed on the continuoushomogenous metal layer surface adjacent the topographical feature.

In another embodiment, the article includes a substrate having asubstrate surface and a topographical feature disposed on and extendingaway from the substrate surface. The topographical feature has a radiusof curvature of 500 nanometers or less. A metal layer is disposed on thesubstrate surface adjacent the topographical feature and on thetopographical feature. A self-assembled monolayer is disposed on themetal layer, and a deposit metal is disposed on the metal layer on thetopographical feature, and not on the metal layer substrate surfaceadjacent the topographical feature.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The Figures, Detail Description and Examples that follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an illustrative method ofmicrofabrication using patterned topography and self-assembledmonolayers;

FIG. 2 is a schematic diagram of another illustrative method ofmicrofabrication using patterned topography and self-assembledmonolayers;

FIG. 3 is a schematic cross-sectional view of an illustrativemicrostructure with deposit metal formed on the microstructure;

FIG. 4 is a scanning electron photomicrograph of the resulting structureformed in Example 1;

FIG. 5 is a scanning electron photomicrograph of the resulting structureformed in Example 2;

FIG. 6 is a photograph of the resulting structure formed in Example 3;and

FIG. 7 is a photograph of the resulting structure formed in Example 4.

While the invention is amenable to various modifications and alternativeforms, specifies thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticle embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION

The present disclosure relates to a method of fabricating patternedmetallic deposits on substrates and the articles so fabricated. Morespecifically, metallic deposits are patterned on substrates having ametallic microstructured surface.

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

“Region” refers to a contiguous fractional portion of an entire surface,e.g., of a substrate surface.

The terms “deposit metal” and “metallic deposit” and “deposited metal”are used interchangeably and refer to a metal deposited on a substrate(i.e., a substrate having a metallic microstructured surface). Thedeposit metal is usually formed from an electroless plating solution.The deposit metal can be in the form of a pattern such as linear tracesin an electrical circuit, contact pads on an electrical device, orlarge-area coatings.

A surface region can be described as having a microstructure or be amicrostructured surface if it includes a topographical feature. A“topographical feature” refers to an intentional geometric deviationfrom smoothness for a substrate surface. It is understood that allsurfaces exhibit some topography, according to a general definition ofthe term, topography. However, a “topographical feature,” as usedherein, does not include a number of types of incidental topography thatwill be familiar to those skilled in the art. A “topographical feature”does not include incidental variations in surface elevation on an atomicscale. A “topographical feature” also does not include the incidental,gradual changes in surface elevation that commonly exist over a largesurface area, with respect to an average elevation over the same surfacearea. For example, “topographical features” do not include smoothlyvarying undulations with “peak-to-valley” height that is substantiallysmaller in size than their spatial separation. A surface that includesonly the aforementioned incidental forms of topography is considerednominally smooth. A nominally smooth surface may be flat or curved,where the curvature is less than 0.1 (micrometer)⁻¹. A “topographicalfeature” can include a protrusive element, an intrusive geometricelement, or both. An example of a linear protrusive geometric elementthat may exist as part of the topographical features of a substratesurface is a peaked ridge that extends above an otherwise nominallysmooth surface. Another example of a linear protrusive geometric elementthat may exist as part of the topographical features of a substratesurface is a square ridge that extends above an otherwise nominallysmooth surface. An example of a linear intrusive geometric element thatmay exist as part of the topographical features of a substrate surfaceis a groove, with square or triangular cross-section for example, thatextends below an otherwise nominally smooth surface.

Depositing a metal “selectively,” refers to depositing metal on onesurface region and not depositing the metal on another surface region.For a metal to be deposited selectively on a substrate surface, it isnot deposited on the entire substrate surface. That is, the depositmetal forms a pattern on the substrate surface. FIGS. 4 to 7 illustrateselective deposition of copper on a gold substrate surface. For example,the metal can be deposited on a topographical feature of a metallicsurface i.e., the metal is not deposited in regions of the metallicsurface that are nominally smooth).

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. Thus, for example, reference to acomposition containing “a metal” includes a mixture of two or moremetals. As used in this specification and the appended claims, the term“or” is generally employed in its sense including “and/or” unless thecontent clearly dictates otherwise.

Unless otherwise indicated, all numbers used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the foregoing specification andattached claims are approximations that can vary depending upon thedesired properties sought to be obtained by those skilled in the artutilizing the teachings of the present invention. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the invention are approximations, the numerical values set forth inthe specific examples are reported as precisely as possible. Anynumerical value, however, inherently contains certain errors necessarilyresulting from the standard deviations found in their respective testingmeasurements.

The invention generally relates to methods for forming patterns ofmetallic deposits (i.e., deposit metal) on substrates having a metallicmicrostructured surface. In some embodiments, the deposit metal iselectrolessly deposited on a substrate only in selected regions on thesurface of the substrate. These selected regions can exhibit a regularor repeating geometric arrangement on the substrate, for example anarray of polygons or a pattern of traces that define discreteundeposited areas that include an array of polygons. In otherembodiments, the selected regions may exhibit a random arrangement onthe substrate, for example a random net of traces that define theboundaries of irregular shapes for undeposited areas. In yet anotherembodiment, the selected regions may exhibit an arrangement that is notregular, repeating, or random, but that is a specified design whichincludes or lacks symmetry or repeating shapes. A deposit metal that ispatterned may exist on only one region of the substrate surface or itmay exist on more than one region of the substrate surface; but to bepatterned it may not exist on all regions of the substrate surface.

A substrate with regions that include a microstructure and regions thatdo not include a microstructure can take a number of different forms. Inone embodiment, the substrate surface may include adjacent regions whichare each smooth and lacking topographical features, and that may lieparallel with each other, but that are elevated or depressed withrespect to each other. This latter configuration necessarily leads to atype of transition region with slope and angles or high curvature withrespect to the aforementioned smooth regions. The transition region candefine a boundary between the smooth regions and be a topographicalfeature. In another embodiment, the substrate surface includes regionsthat are smooth and that lack microstructure, together with regions thatcan be described as having a microstructure in the form of a texture.This texture can include defined geometric elements such as ridges,pyramids, posts, or grooves. Alternatively, the texture may includerandomly shaped geometric elements. Surface regions includingmicrostructure where the microstructure is a texture can have associatedwith them a spatially averaged elevation with respect to the regions ofthe surface that are smooth, possibly flat, and lacking topographicalfeatures. Spatially averaged elevation of textured regions of thesubstrate surface may lied below or above the elevation of adjacentsmooth and possibly flat regions of the substrate surface. Such texturedregions can recess from or protrude from the adjacent regions,respectively.

A patterned metallic deposit on a substrate, where the arrangement ofsurface regions that include the metallic deposit is determinedaccording to the topographical features of the substrate, may exhibitone of a number of spatial relationships to the topographical features.For example, for regions that include topographical features, eachregion can include a single geometric element spaced apart by adjacentregions that lack topographical features, and the patterned metallicdeposit may be selectively deposited onto the individual topographicalfeatures. In such a case, the pattern of the metallic deposit would besubstantially identical to the pattern of the individual topographicalfeatures. Alternatively, if topographical features are closely spaced ina region of the substrate, the metallic deposit may bridge individualgeometric or topographical elements in the regions includingtopographical features. If a substrate surface includes regions withmicrostructure in the form of texture that is made up of multipleclosely spaced topographical features, together with regions that lacksuch microstructure, a patterned metallic deposit may bridge the closelyspaced topographical features leading to a contiguous deposit in theentire region with microstructure in the form of the texture.

Methods for generating articles with structured surfaces include, forexample, the use of a mechanical tool, depositing material onto asubstrate, or removing material from a substrate. Illustrativemechanical tools form a microstructured surface by embossing, scribing,or molding the microstructure onto the substrate surface.

A partial listing of illustrative methods for generating articles withstructured surfaces includes diamond machining (M. A. Davies, C. J.Evans, S. R. Patterson, R. Vohra, and B. C. Bergner, “Application ofPrecision Diamond Machining to the Manufacture of Micro-photonicsComponents,” Proc. of SPIE 5183 94-108 (2003)), optical lithography,e-beam lithography, x-ray lithography, laser beam writing, electron beamwriting, and laser ablation (E. B. Kley, “Continuous Profile Writing byElectron and Optical Lithograph,” Microelectronic Engineering 34 261-298(1997)). Methods for generating a structured surface may include a stepwhere material is exposed to light, X-rays, or electrons and thendeveloped and selectively removed, or a step where a material is etched(Y. Hagiwara, N. Kimura, and K. Emori, U.S. Pat. No. 4,865,954 “Processfor Formation of Metallic Relief” (1989)). Material (e.g., metal) can beselectively added onto the substrate surface, to form a structuredsurface, by convention methods including, for example, sputtering, vapordeposition, and the like. Material (e.g. metal) can be removed from thesubstrate to form a structured surface, by convention methods including,for example, etching and the like. These addition and removal methodscan be combined with other methods such as, for example,photolithography methods and lift-off methods.

Particularly advantageous approaches for the preparation of a structuredsurface include replication or forming a microstructure with amechanical tool. Mechanical tools form a microstructured surface byembossing, scribing, or molding the microstructure onto the substratesurface. Replication includes the transfer of surface structural featurefrom a master tool to another material and includes embossing ormolding. Methods involving replication are noteworthy for the ease andspeed with which materials with structured surfaces can be generated.Also noteworthy is the small size that can be achieved for surfacestructure features that are generated through replication. Nanoscalefeatures with size less than 10 nanometers, can be replicated (S. R.Quake and A. Scherer, “From Micro- to Nanofabrication with SoftMaterials,” Science 290 1536-1540 (2000); V. J. Schaeffer and D. Harker,“Surface Replicas for Use in the Electron Microscope,” Journal ofApplied Physics 13, 427-433 (1942); and H. Zhang and G. M. Bensen, WO0168940 A1, “Methods for replication, replicated articles, andreplication tools” (2001)).

Replication can be achieved in any number of ways. One illustrativemethod for replicating the surface structural features of a mastermechanical tool into the surface of another material is through thermalembossing (M. J. Ulsh, M. A. Strobel, D. F. Serino, and J. T. Keller,U.S. Pat. No. 6,0986,247 “Embossed Optical Polymeric Films” (2000); andD. C. Lacey, U.S. Pat. No. 5,932,150 “Replication of Diffraction Imagesin Oriented Films” (1999)). Thermal embossing involves the pressing of amaster mechanical tool against a deformable material, causing thesurface structure of the master tool to deform the surface of thedeformable material, thereby generating a negative replica of thatmaster tool surface. Materials that can be embossed with surfacestructure include, for example, soft metals and organic materials suchas polymers. Examples of soft metals that can be embossed includeindium, silver, gold, and lead. Polymers suitable for thermal embossinginclude thermoplastics. Examples of thermoplastics include polyolefins,polyacrylates, polyamides, polyimides, polycarbonates, and polyesters.Further examples of thermoplastics include polyethylene, polypropylene,polystyrene poly(methylmethacrylate), polycarbonate of bisphenol A.poly(vinyl chloride), poly(ethylene terephthalate), and poly(vinylidenefluoride). For the preparation of thermally embossed materials, it isoften convenient and useful to start with material in film form.Optionally, a film for embossing can include multiple layers (J. Fitch,J. Moritz, S. J. Sargeant, Y. Shimizu, and Y. Nishigaki, U.S. Pat. No.6,737,170 “Coated Film with Exceptional Embossing Characteristics andMethods for Producing It” (2004); and W. W. Merrill, J. M. Jonza, O.Benson, A. J. Ouderkirk, and M. F. Weber, U.S. Pat. No. 6,788,463,“Post-Formable Multilayer Optical Films and Methods of Forming” (2004)).

Another approach for replicating the surface structure of a mastermechanical tool into the surface of polymer is to cure a flowableprecursor to the polymer while in contact with the master mechanicaltool. Curing a flowable precursor to a polymer while in contact with themaster mechanical tool is one form of molding. Examples of flowableprecursors include neat monomers, mixtures of monomers, solutions ofmonomers or polymers that may include removable solvent, anduncrosslinked polymers. Generally, a precursor to the cured polymer canbe cast onto a master mechanical tool or into a mold, following bycuring (J. A. Martens, U.S. Pat. No. 4,576,850 “Shaped Plastic ArticlesHaving Replicated Microstructure Surfaces” (1986)). Curing refers to thedevelopment of increased elastic modulus, usually by way of a chemicalreaction. Curing to develop elastic modulus can include heating,addition of a catalyst, addition of an initiator, or exposure toultraviolet light, visible light, infrared light, X-rays, or an electronbeam. Once the polymer has been cured, it can be removed as a solid fromcontact with the master tool or mold. Examples of polymers suitable formolding include polyacrylates, polyimides, epoxies, silicones,polyurethanes, and some polycarbonates.

Another illustrative method for generating a microstructure pattern onthe surface of a substrate using a mechanical tool is by scribing.“Scribing” refers to the application of a stylus to an otherwiseunstructured surface and pressing or translating the stylus on thesurface, generating surface microstructure. A stylus tip may be made ofany material such as, for example, a metal, ceramic, or polymer. Astylus tip may include diamond, aluminum oxide, or tungsten carbide. Astylus tip may also include a coating, for example a wear-resistantcoating such as titanium nitride.

The substrate can be prepared from any suitable material. In someembodiments, the substrate is made of metal or organic materials such aspolymers. Examples of metal include indium, silver, gold, and lead.Examples of polymers include thermoplastic polymers. Examples ofthermoplastic polymers include polyolefins, polyacrylates, polyamides,polycarbonates, and polyesters. Further examples of thermoplasticsinclude polyethylene, polypropylene, polystyrene,poly(methylmethacrylate), polycarbonate of bisphenol A. poly(vinylchloride), poly(ethylene terephthalate), and poly(vinylidene fluoride).

In other embodiments, the substrate can be prepared from glasses,glass-ceramics, ceramics, semiconductors, or combinations thereof.Examples of useful glasses include silicates, germanates, phosphates,and chalcogenides. Among silicates, soda-lime-silica and borosilicateglasses can be useful. Fused silica also can be a useful substratematerial Germanate and chalcogenide glasses are particularly useful forapplications where increased infrared transmission is desired, comparedwith silicate glasses. Phosphate glasses generally exhibit convenientlylow forming temperatures, but often also exhibit lower chemicaldurability. Other network-formers and modifiers in useful glassesinclude aluminum oxide, antimony pentoxide, tantalum oxide, niobiumoxide, lead oxide, bismuth oxide, zinc oxide, magnesium oxide, strontiumoxide, barium oxide, lithium oxide, and potassium oxide. Glass-ceramicsthat include a crystallized microstructure are also useful as substratematerials. Examples of useful glass-ceramics include lithium disilicate,beta-quartz, enstatite, cordierite, spinel, beta-spodumene,beta-eucryptite, and apatite compositions. Glass-ceramics offer the easeof glass-formability, together with high strength and toughness.Substrates can also include ceramics. Examples of useful ceramicsinclude oxides, nitrides, borides, and carbides. Examples of usefulceramics include barium titanate, barium strontium titanate, leadzirconate titanate, bismuth titanate, aluminum oxide, beryllium oxide,aluminum nitride, silicon nitride, and silicon carbide. Substrates canalso include semiconductors. Examples of useful semiconductors includeGroup IV elements, binary compounds of Group II and Group VI elements,binary compounds of Group III and Group V elements, and their variousalloys. Some useful semiconductors include silicon, germanium, galliumarsenide, indium phosphide, zinc sulfide, and cadmium telluride.Substrates can be prepared from more than one class of these materials.For example, substrates can include a semiconductor crystal with acoating of a glass or ceramic material.

A “self-assembled monolayer” refers to a single layer of molecules thatare attached (e.g., by a chemical bond) to a surface and that haveadopted a preferred orientation with respect to that surface.Self-assembled monolayers have been shown to cover surfaces socompletely that the properties of that surface are changed. For example,application of a self-assembled monolayer can result in a surface energyreduction.

Examples of chemical species that are suitable for formingself-assembled monolayers include organic compounds such as organosulfurcompounds, silanes, phosphonic acids, benzotriazoles, and carboxylicacids. Examples of such compounds are discussed in the review by Ulman(A. Ulman, “Formation and Structure of Self-Assembled Monolayers,” Chem.Rev. 96 1533-1554 (1996)). In addition to organic compounds, certainorganometallic compounds are useful for forming self-assembledmonolayers. Examples of organosulfur compounds that are suitable forforming self-assembled monolayers include alkyl thiols, dialkyldisulfides, dialkyl sulfides, alkyl xanthates and dialkylthiocarbamates.Examples of silanes that are suitable for forming self-assembledmonolayers include organochlorosilanes and organoalkoxysilanes. Examplesof phosphonic acid molecules that are suitable for formingself-assembled monolayers are discussed by Pellerite et al. (M. J.Pellerite, T. D. Dunbar, L. D. Boardman, and E. J. Wood, “Effects ofFluorination on Self-Assembled Monolayer formation from AlkanephosphonicAcids on Aluminum: Kinetics and Structure,” Journal of PhysicalChemistry B 107 11726-11736 (2003)). Chemical species that are suitablefor forming self-assembled monolayers can include, for example,hydrocarbon compounds, partially fluorinated hydrocarbon compounds, orperfluorinated compounds. The self-assembled monolayer can include twoor more different chemical species. In the use of two or more differentchemical species, the chemical species may exist in the self-assembledmonolayer as a mixture or with a phase-separated morphology.

Illustrative useful molecules for forming a self-assembled monolayerinclude, for example, (C₃-C₂₀)alkyl thiols, (C₁₀-C₂₀)alkyl thiols or(C₁₅-C₂₀)alkyl thiols. The alkyl groups can be linear or branched andcan be substituted or unsubstituted with substituents that do notinterfere with the formation of a self-assembled monolayer.

The self-assembled monolayer can be formed on a metal surface using avariety of methods. For example, the metal surface can be dipped into asolution that contains the chemical species, the metal surface can besprayed with a solution that contains the chemical species, or the metalsurface can be exposed to the chemical species in a vapor phase. Anyexcess of the chemical species that is not attached to the metal surfacecan be removed, for example, by rinsing with a suitable solvent.

Metallic surfaces can be used to support a self-assembled monolayer. Themetal surface can include, for example, elemental metal, metal alloys,intermetallic compounds, metal oxides, metal sulfides, metal carbides,metal nitrides, and combinations thereof. Exemplary metallic surfacesfor supporting self-assembled monolayers include gold, silver,palladium, platinum, rhodium, copper, nickel, iron, indium, tin,tantalum, as well as mixtures, alloys, and compounds of these elements.

The term “electroless deposition” refers to a process for theautocatalytic plating of metals. It typically involves the use of anelectroless plating solution that contains a soluble form of the depositmetal together with a reducing agent. The soluble form of the depositmetal is usually an ionic species or a metal complex (i.e., a metalspecies coordinated to one or more ligands). In may embodiments,electroless deposition does not include the application of electricalcurrent to a work piece that is being coated. The volume by Mallory andHajdu describes the process in detail (Electroless Plating—Fundamentalsand Applications, Ed. G. O. Mallory and J. B. Hajdu, William AndrewPublishing, Norwich (1990)). The steps involves in electroless platinginclude the preparation of a substrate with a catalytic surface (e.g., ametallic microstructured surface), followed by immersion of thesubstrate in an appropriate plating bath. The catalytic surfacecatalyzes the deposition of metal from solution. Once started, platingproceeds by the continued reduction of the solution metal source,catalyzed by its own metal surface, hence the term “autocatalytic.”Metallic deposits that can be formed using electroless depositioninclude copper, nickel, gold, silver, palladium, rhodium, ruthenium tin,cobalt, zinc, as well as alloys of these metals with each other or withphosphorous or boron, as well as compounds of these metals with eachother or with phosphorous or boron. Suitable reducing agents include,for example, formaldehyde, hydrazine, aminoboranes, and hypophosphite.Suitable metallic microstructured surfaces for catalysis of electrolessdeposition include palladium, platinum, rhodium, silver, gold, copper,nickel, cobalt, iron, and tin, as well as alloys and compounds of theelements with each other or with other elements. The deposit metal andthe metal included in the metallic microstructure surface can be thesame or different.

Not wishing to be bound by any particular theory, it is presumed that atopographical feature on a surface can be sufficiently disruptive to thestructure of a self-assembled monolayer attached to the surface suchthat the ability of the self-assembled monolayer to alter the propertiesof that surface is compromised. For example, a gold surface is known tohave the property of supporting self-assembled monolayers and theproperty of catalyzing electroless deposition of metals. In the past, ithas been shown that a self-assembled monolayer on gold will block itscatalytic activity with regard to electroless plating (A. Kumar and G.M. Whitesides, U.S. Pat. No. 5,512,131, “Formation of MicrostampedPatterns on Surfaces and Derivative Articles,” (1996)).

Further, it is presumed that the topographical features for a metalsurface such as gold can interfere with that ability for self-assembledmonolayers to block the catalytic activity, thus forming the basis formethods of patterning. The topographical features that lead to suchapparent disruption in catalytic activity can be generated through theconvenient methods of embossing, scribing, or molding.

FIG. 1 is a schematic diagram of an illustrative method ofmicrofabrication using patterned topography and self-assembledmonolayers. A substrate 105 includes a metal layer 110 disposed on thesubstrate 105. In one embodiment, the substrate 105 is formed from apolymeric material and the metal layer 110 is formed from a metal. Inmany embodiments, the metal layer 110 is a continuous homogenous metallayer. In one embodiment, the continuous homogenous metal layer 110 isformed from a single metal or alloy.

A mechanical tool 120 is shown having a topographical feature 130 formedon a first surface 135 of the mechanical tool 120. The mechanical tool120 can be applied to a surface 140 of the metal layer 110 such that themechanical tool 120 first surface 135 is in contact with the surface 140of the metal layer 110. In one embodiment pressure (as shown by thedownward arrows) is applied to the mechanical tool 120 such that anegative replica of the microstructure or topographical feature 120 istransferred to or embossed onto the surface 140 of the metal layer 110forming a microstructure 131 on the metal layer 110 surface 140. Thismechanically formed microstructure 131 is termed a metallicmicrostructured surface 136. A microstructured article 101 includes thesubstrate having a metallic microstructure surface 136.

A self-assembled monolayer 150 is formed 102 on the metallicmicrostructured surface 136, as described above. In this embodiment, theself-assembled monolayer 150 is shown disposed across the entire surface140 of the metal layer 110. The self-assembled monolayer 150 can beuniformly disposed along the metal layer 110 surface 140. Theself-assembled monolayer 150 can have areas of disruption on or adjacentto the microstructure 131. In at least some embodiments, the areas ofdisruption on or adjacent to the microstructure 131 are caused by themicrostructure 131 topography.

The self-assembled monolayer 150 is exposed 103 to an electrolessplating solution 160 including a soluble form of a deposit metal. Thedeposit metal can be deposited 104 selectively on the metallicmicrostructured surface 136 to form a deposit metal pattern 165. In oneembodiment, the deposit metal includes copper and the metallicmicrostructured surface 136 is formed from gold. In some embodiments, atleast a portion of the metal layer 110 can be removed via etching afterdeposition of the deposit metal.

While not wishing to be bound by any particular theory, it is believedthat the areas of disruption in the self-assembled monolayer 150 allowthe deposit metal to bond with the metal layer 140 at the disruptionareas formed on or near the microstructures 131.

FIG. 2 is a schematic diagram of another illustrative method ofmicrofabrication using patterned topography and self-assembledmonolayers. A mechanical tool 220 is shown having a topographicalfeature 230 formed on a first surface 235 of the mechanical tool 220.The mechanical tool can be applied to a surface 206 of a substrate 205such that the mechanical tool 220 first surface 235 is in contact withthe surface 206 of the substrate 205. In one embodiment pressure (asshown by the downward arrows) is applied to the mechanical tool 220 suchthat the microstructure or topographical feature 230 is transferred tothe surface 206 of the substrate 205 forming 201 a microstructure 208 onthe substrate 205 surface 206. This mechanically formed microstructure208 is termed a substrate microstructured surface 207.

A metal layer 210 is then disposed 202 on the substrate microstructuredsurface 207 to form a metallic microstructured surface 236. In oneembodiment, the substrate 205 is formed from a polymeric material andthe metal layer 20 is formed from a metal. In many embodiments, themetal layer 210 is a continuous homogenous metal layer. In oneembodiment, the continuous homogenous metal layer 210 is formed from asingle metal or alloy.

A self-assembled monolayer 250 is formed 202 on the metallicmicrostructured surface 236, as described above. The self-assembledmonolayer 250 is shown disposed on the entire surface 240 of the metallayer 210. In one embodiment, the self-assembled monolayer 250 isuniformly disposed along the metal layer 210 surface 240. Theself-assembled monolayer 250 can have areas of disruption on or adjacentto the microstructure 231. In at least some embodiments, the areas ofdisruption on or adjacent to the microstructure 231 are be caused by themicrostructure 231 topography.

The self-assembled monolayer 250 is exposed 203 to an electrolessplating solution 260 including a soluble form of a deposit metal. Thedeposit metal can be deposited 204 selectively on the metallicmicrostructured surface 236 to form a deposit metal pattern 265. In oneembodiment, the deposit metal includes copper and the metallicmicrostructured surface 236 is formed from gold. In some embodiments, atleast a portion of the metal layer 210 can be removed via etching afterdeposition of the deposit metal.

While not wishing to be bound by an particular theory, it is believedthat the areas of disruption in the self-assembled monolayer 250 allowthe deposit metal to bond with the metal layer 240 at the disruptionareas formed on or near the microstructures 231.

FIG. 3 is a schematic cross-sectional view of an illustrativemicrostructure with deposit metal 365 formed on the microstructure. Ametallic microstructured surface 336 includes a smooth region 330adjacent a topographical feature 320. The topographical feature 320 isshown as a protrusive feature extending away from the substrate. In thisembodiment, the smooth region 330 and the topographical feature 320 areformed of a single continuous homogenous metal layer 336. Aself-assembled monolayer 350 is disposed on the single continuoushomogenous metal layer 336. A deposit metal 365 is selectively formed atareas of disruption 361 on the topographical feature 320 via anelectroless plating bath 360.

In some embodiments, the topographical feature 30 extends away from thesubstrate and has a radius of curvature R of 500 nanometers or less, orfrom 5 to 500 nanometers, or from 10 to 500 nanometers, or from 20 to250 nanometers, or from 50 to 200 nanometers. The radius of curvature Rcan be measured, for example, with the aid of a scanning probemicroscope, for example an atomic force microscope.

In many embodiments, useful topographical features that protrude fromthe substrate surface can have height ranging from 1 nanometers to 100micrometers, or from 10 nanometers to 10 micrometers, or from 20nanometers to 1 micrometer.

The deposit metal may be described as having an area shape and an areasize on the substrate surface as well as a thickness. The area shape ofthe deposit metal can exhibit a regular or repeating geometricarrangement on the substrate, for example an array of deposit metalpolygons or a pattern of deposit metal traces that define the boundariesof discrete undeposited areas that include an array of polygons. Inother embodiments, the deposit metal shapes may exhibit a randomarrangement on the substrate, for example a random net of traces thatdefine the boundaries of irregular shapes for undeposited areas. In yetanother embodiment, the deposit metal shapes may exhibit an arrangementthat is not regular, repeating, or random, but that is a specifieddesign which includes or lacks symmetry or repeating geometric elements.In one embodiment, a shape for the deposit metal that is useful formaking a light-transmitting, EMI shielding material is a square grid,which includes traces of the deposit metal characterized by a width,thickness, and pitch. Other useful shapes for making alight-transmitting, EMI shielding material include continuous metallictraces that define open areas that have the shape of a regular hexagonand that are arranged in closely packed order.

In some embodiments, the smallest area dimension for the deposit metalshapes, for example the width of a linear trace of deposit metal, canrange from 1 nanometer to 1 millimeter or from 10 nanometers to 50micrometers, or from 100 nanometers to 25 micrometers, or from 1micrometer to 15 micrometers. In one illustrative embodiment for makinga light-transmitting EMI shielding material, the width of linear tracesof deposit metal is in a range from 5 micrometers to 15 micrometers, thethickness is in a range from 1 micrometer to 5 micrometers, and thepitch is in the range from 25 micrometers to 1 millimeter. The largestarea dimension for the deposit metal shapes above, for example thelength of a linear trace of deposit metal, can range from 1 micrometerto 5 meters, or from 10 micrometers to 1 meter. For making alight-transmitting EMI shielding material, a sheet of EMI shieldingmaterial, the length of linear traces of deposit metal can be in therange from 1 centimeter to 1 meter, for example.

The present invention should not be considered limited to the particularexamples described herein, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention can be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

EXAMPLES

Unless otherwise noted, chemical reagents and solvents were or can beobtained from Aldrich Chemical Co., Milwaukee, Wis.

As used herein, “FM-2” refers to gold-coated poly(ethyleneterephthalate) film available from CPFilms, Canoga Park, Calif.

Electroless Copper Plating Solution

An electroless copper plating solution was prepared by combiningdeionized water (199.29 g), cupric sulfate pentahydrate (1.50 g), sodiumhydroxide (1.35 g), formaldehyde (1.32 g of a 37 weight percent aqueoussolution, available from Mallinckrodt Baker Inc., Phillipburg, N.J.),N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (2.31 g; availablefrom Lancaster Synthesis Inc., Pelham, N.H.), ethylenediaminetetraaceticacid (1.7 g), and 2,2′-bipyridine (0.03 g). The pH of the resultantsolution was adjusted to 12.3 using 2.0 moles per liter aqueous sodiumhydroxide solution. The plating solution was used at a temperature of68° C.

Example 1

Deposition of Copper on a Substrate Patterned by Mechanical Scribing

The gold coating of a 1 inch (25.4 mm) by 1.5 inch (38.1 mm) sample ofFM-2 was scribed in a rectangular grid pattern using an OMNISCRIBEdiamond-tipped scribe (available from Lunzer, Inc., Saddle Brook, N.J.).The film sample was immersed in a 0.1 weight percent solution of1-octadecanethiol in ethanol for 2 minutes, after which time it wasrinsed with ethanol. The film sample was then immersed in theelectroless copper plating solution at 68° C. After 30 minutes, the filmsample was removed from the electroless copper plating solution, rinsedwith deionized water, and allowed to dry in air at room temperature. Aportion of the surface of the sample is shown in FIG. 4. In FIG. 4, thelight-tinted regions are regions where copper was deposited.

The film sample was then immersed for approximately 15 seconds in asolution made by dissolving potassium iodide (2 g) and then iodine (1 g)in deionized water (40 mL) to remove by etching the exposed gold coatingon the film. The film sample was then rinsed with deionized water andwas allowed to dry in air at room temperature.

Example 2

Deposition of Copper on a Substrate Patterned by Mechanical Scribing

The gold coating of a 1 inch (25.4 mm) by 1.5 inch (38.1 mm) sample ofFM-2 was randomly scribed using a CUT-CAT rotary paper trimmer(available from Dahle North America, Inc. Peterborough, N.H.). The filmsample was immersed in a 0.1 weight percent solution of1-octadecanethiol in ethanol for 2 minutes, after which time it wasrinsed with ethanol. The film sample was then immersed in theelectroless copper plating solution at 68° C. After 30 minutes, the filmsample was removed from the electroless copper plaint solution, rinsedwith deionized water, and allowed to dry in air at room temperature. Aportion of the surface of the sample is shown in FIG. 5. In FIG. 5, thelight-tinted regions are regions where copper was deposited.

Example 3

Deposition of Copper on a Substrate Patterned by Mechanical Scribing

The gold coating of a 1 inch (25.4 mm) by 1.5 inch (38.1 mm) sample ofFM-2 was scribed in a pattern of approximately parallel lines using arotary glass cutter (available from Fletcher-Terry Co., Farmington,Conn.). The film sample was partially immersed in a 0.1 weight percentsolution of 1-octadecanethiol in ethanol for 2 minutes, after which timeit was rinsed with ethanol. The film sample was then partially immersedin the electroless copper plating solution at 68° C. After 30 minutes,the film sample as removed from the electroless copper plating solution,rinsed with deionized water, and allowed to dry in air at roomtemperature. The surface (i.e., the entire surface) of the sample isshown in FIG. 6. In FIG. 6, the light-tinted approximately parallellines are regions where copper was deposited.

Example 4

Deposition of Copper on a Substrate Patterned by Embossing

A glass embossing tool was made by etching a pattern onto a glass plate.A glass plate having dimensions of 12.7 cm by 7.6 cm by 0.05 cm wascovered on one surface with one layer of 3M Polyimide Film Tape 5413(available from 3M Company, St. Paul, Minn.) in a region havingdimensions of about 3 cm by 4 cm. After it was applied to the glassplate, the tape was cut with a razor blade to provide approximately 0.05cm wide strips of tape at intervals of approximately 0.07 cm. The tapebetween the approximately 0.05 cm wide strips was removed, leaving theglass plate with a series of approximately 0.5 cm by approximately 4 cmstrips of tape adhered to one surface. The glass plate was thensubmerged in a 25 weight percent aqueous solution of hydrofluoric acidfor 10 minutes. After the glass plate was removed from the acid solutionand was rinsed with water, it was allowed to dry in air at roomtemperature. The strips of polyimide tape were removed to reveal thatthe portion of glass plate that was not covered by the strips of tapewas etched and removed by the hydrofluoric acid. The glass plate had apattern of approximately 0.05 cm wide ridges that were approximately0.06 cm high. The surface of the glass that included the ridges waslightly abraded using a Model Somaca BM-106G-RP24 belt sander (availablefrom Sommer & Maca Industries, Chicago, Ill.) with a flexible M74 gradediamond belt (available from 3M Company, St. Paul, Minn.).

The glass embossing tool was used to make an embossed acrylic sheet byplacing an approximately 3.8 cm by 7.6 cm by 0.3 cm piece of OPTIXacrylic sheet (available from Plaskolite, Inc. Columbus, Ohio) againstthe glass plate with the sheet contacting the pattern of ridges on theglass. The glass embossing tool and acrylic sheet assembly was placedbetween the heated platens of a Model AUTO M laminating press (availablefrom Carver, Inc., Wabash, Ind.) at 130° C. for 30 minutes. Then, usingthe press, the glass embossing tool was pressed into the acrylic sheetsusing 3560 Newtons of force at a temperature of 130° C. for 20 minutes.After the glass/sheet assembly was removed from the press and theembossed sheet had cooled to room temperature, the embossed side of theacrylic sheet (that is, the side that was pressed against the glassembossing tool) was sequentially coated with 50 Angstroms of titaniumand then 600 Angstroms of gold using a thermal evaporate or (availablefrom Kurt J. Lesker Co., Pittsburgh, Pa.).

The metal coated embossed acrylic sheet was immersed in a 0.0 weightpercent solution of 1-octadecanethiol in ethanol for 2 minutes, afterwhich time it was rinsed with ethanol. The film sample was then immersedin the electroless copper plating solution at 68° C. After 30 minutes,the film sample was removed from the electroless copper platingsolution., rinsed with deionized water, and allowed to dry in air atroom temperature. A portion of the surface of the sample is shown inFIG. 7. In FIG. 7, the light-tinted regions are regions where copper wasdeposited.

1. An article comprising: a substrate having a substrate surface and atopographical feature comprising a protrusive and an intrusive elementthat is part of the substrate, said protrusive element having a heightranging from 1 nanometer to 100 micrometers above the surface disposedon the substrate surface; a continuous homogenous metal layer disposedon the substrate surface adjacent the topographical feature and on thetopographical feature; a self-assembled monolayer disposed on thecontinuous homogenous metal layer; and a deposit metal disposed on thecontinuous homogenous metal layer on the topographical feature, and notdisposed on the continuous homogenous metal layer substrate surfaceadjacent the topographical feature.
 2. An article according to claim 1wherein the substrate comprises a polymeric material.
 3. An articleaccording to claim 1 wherein the continuous homogenous metal layercomprises gold, silver, a gold alloy, or a silver alloy.
 4. An articleaccording to claim 1 wherein the deposit metal comprises copper or acopper alloy.
 5. An article comprising: a substrate having a substratesurface and a topographical feature, that is part of the substrate,disposed on and extending away from the substrate surface, thetopographical feature having a height ranging from 10 nanometers to 10micrometers above the surface and having a radius of curvature of 500nanometers or less; a metal layer disposed on the substrate surfaceadjacent the topographical feature and on the topographical feature; aself-assembled monolayer disposed on the metal layer; and a depositmetal disposed on the metal layer on the topographical feature, and notdisposed on the metal layer substrate surface adjacent the topographicalfeature.
 6. An article according to claim 5 wherein the topographicalfeature has a radius of curvature in a range of 50 to 250 nanometers. 7.An article according to claim 5 wherein the self-assembled monolayercomprises a (C₃-C₂₀)alkyl thiol.
 8. An article according to claim 5wherein the substrate comprises a polymeric material.
 9. An articleaccording to claim 5 wherein the metal layer comprises gold, silver, agold alloy, or a silver alloy.
 10. An article according to claim 5wherein the deposit metal comprises copper or a copper alloy.